Advance in objective investigation can only be made through limitation of enquiry to specific fields. To be fruitful, an enquiry into any aspect of human behaviour needs instruments capable of revealing facts relevant to the nature of the enquiry. There is an intimate connection in the progress of all forms of objective study between instruments used in an investigation and the achievement of a new understanding of the subject investigated.
Much knowledge has already been won in the fields of child psychology and child psychotherapy and we already possess a considerable store of information concerning the relation of children to their human environment, to their own developing physical powers, to each other, and to external objects. The psychotherapies of Freud, Jung & Adler have brought us information concerning the development of the instinctive drives and their relation to the ego components, concerning the influence upon a child of factors of racial and parental emotion and of the effect upon a child’s life of his own self valuation.